The use of radio communications systems to communicate is pervasive in modem society. At least part of the communication path extending between a set of communication stations in a radio communication system is defined upon a radio link. Use of the radio link frees the communication stations from the conventional requirement of a wireline communications system that a fixed wireline connection extend along the entire communication path between the communication stations. Improved communication mobility is provided, and the use of a radio link permits communication stations to be positioned and used at locations at which wireline connections would be impractical.
A cellular communication system is an exemplary type of radio communication system. Successive generations of communication systems have been developed and deployed. And, their use is widespread, sometimes having penetration levels that approach, or exceed, those of conventional wireline networks. While, initially, cellular communication systems were used primarily for voice communications, increasingly, cellular communication systems are used to effectuate data communication services. In a typical cellular communication system, a mobile station is used through which to communicate. The mobile station communicates with a network part of the communication system that, in turn, is connected to a PSTN (public-switched, telephonic network) or a data network, such as the Internet.
Channel allocations are made to a mobile station to permit its communication pursuant to some types of communication sessions. The allocation of channels typically involves exchange of signaling between the mobile station and the radio network with which the mobile station communicates. Signaling is used, not only pursuant to channel allocation, but also, importantly, to synchronize the mobile station with the radio network. Particularly when digital communication techniques are used, time synchronization of the mobile station with the network is critical. Without appropriate synchronization of the mobile station with the network, communications are generally unable to be carried out adequately. Accordingly, cellular communication systems provide schemes by which to permit the synchronization of a mobile station with a network with which the mobile station is to communicate.
For instance, in a GSM/EDGE (global system for mobile communications/enhanced data for GSM evolution)—compliant, cellular communications system, both a FCCH (frequency correction channel) and SCH (synchronization channel) are defined. Control signals broadcast by the network upon such defined channels are detected by the mobile station and used by the mobile station pursuant to synchronization of the mobile station with the network. Existing methods generally utilize a sequential procedure, that is, a procedure in which the FCCH is first monitored and in which, thereafter, the SCH is monitored.
In one conventional scheme, for instance, the two-step, sequential monitoring is carried out. A problem sometimes results due to false detections made when monitoring the FCCH. Positional and frequency offset information is broadcast on the FCCH. This information is needed to obtain additional information from the SCH. If the FCCH information is erroneous, a false detection results. That is to say, when the erroneous information is used to monitor the SCH to obtain SCH burst information broadcast thereon, the SCH burst information shall correspondingly be erroneous, and, presumptively, decoding of the obtained SCH burst information is unsuccessfully carried out. Upon determination that the SCH burst information is unsuccessfully decoded, the procedure is repeated. The FCCH is again monitored, again to obtain positional and frequency offset information that is then used pursuant to SCH monitoring to detect, obtain, and decode the SCH burst information.
In another conventional scheme, false, i.e., erroneous, FCCH detections, and their associated problems, are reduced. In this scheme, the two-stage, FCCH search-then-SCH-decode procedure is performed only to find the first ARFCN (absolute radio frequency channel number), of the network. Once the ARFCN and is obtained, a frequency offset of the network is derived. And, an assumption is made that the subsequent ARFCNs all have the same frequency offset. Subsequent synchronization attempts bypass the FCCH monitoring and detection steps. Instead, a search is directly made at the SCH or the SCH burst information. As the SCH burst is structurally more complex than that of the FCCH burst, false detections are less likely to occur. However, the search on the SCH for the SCH burst information fails if the ARFCNs have large frequency offsets from one another.
An improved manner by which to synchronize a mobile station to the radio network would therefore be advantageous.
It is in light of this background information related to synchronization of a mobile station to a radio network that the significant improvements of the present invention have evolved.